bio-medical instruments.....HEART RATE MONITOR

 Heart rate monitor:
A heart rate monitor is a  device which allows a subject to measure his or her heart rate in real time or record his or her heart rate for study
The first wireless EKG Heart rate monitor was invented in 1977 as a training aid for the Finnish National Cross Country Ski team and as 'intensity training' became a popular concept in athletic circles in the mid-80s, retail sales of wireless personal heart monitors started from 1983.

The heart is one of the most vital organs within the human body. It acts as a pump that circulates oxygen and nutrient carrying blood around the body in order to keep it functioning. The circulated blood also removes waste products generated from the body to the kidneys. When the body is exerted the rate at which the heart beats will vary proportional to the amount of effort being exerted. By detecting the voltage created by the beating of the heart, its rate can be easily observed and used for a number of health purposes
An electrocardiogram (ECG) is a graphical trace of the voltage produced by the heart. A sample trace of a typical ECG output for a single beat is shown below. There are 5 identifiable features in an ECG trace which corresponds to different polarisation stages that makes up a heart beat. These deflections are denoted by the letters P, Q, R, S and T.
Figure

By detecting the R peaks and measuring the time between them the heart rate can be calculated and then displayed.

to amplify the desired weak signal in the presence of noise from other muscles and electrical sources. A display of the heart rate will be obtained by measuring the time between signal peaks and then calculating the frequency of the peaks in units of beats per minute.